Currently, a U-shaped alternating-current permanent magnet synchronous motor is often applied to a drainage pump, and thus such a drainage pump is often referred to as an alternating-current permanent magnet drainage pump. Such a drainage pump is generally applied to a washing machine or a dishwasher. Since such a drainage pump has a difficulty in starting at a low voltage, the electromagnetic efficiency is thereby limited, and the overall efficiency of the product is low. On the other hand, in recent years, with manufacturers are growing in number, market competition are getting fiercer, and customer requirements are rising higher, pressure on the costs of products has been highlighted, and the noise and vibration problems need to be improved.
During operation of a conventional U-shaped alternating-current permanent magnet drainage pump, there is vibration and collision between coils and a stator core to induce noise. On the other hand, due to presence of a rotor cylinder between the stator core and a rotor, both a thickness of the rotor cylinder itself and a required reasonable gap between the stator core and the rotor shall increase a distance between the stator core and the rotor. Thereby, air gap is increased, operation efficiency is affected, and a size of a pump body is increased, which produces a non-negligible effect for a micro-sized pump.
FIG. 1 shows a structure of a pump shell of a conventional U-shaped alternating-current permanent magnet synchronous motor. As shown in FIG. 1, the pump includes a rotor cylinder 9′ in a cylindrical shape, and a core assembly is disposed in an inner cavity of the rotor cylinder. The rotor cylinder is usually made of plastic, with a thickness of 1 mm. Due to the presence of the rotor cylinder, the air gap between the stator core and the rotor magnetic core is increased.
FIGS. 1a and 1b show an alternating-current permanent magnet drainage pump in the prior art. In which, fabricated coils 7′ are loaded in a plastic mold to perform injection molding to form a coil package 5′. The injection molding process performed to the coils 7′ is same as an injection molding process performed to coils being disclosed in Chinese patent No. 200710143209.3 and titled “A permanent magnet synchronous motor for a drainage pump”. That is, after the coil package 5′ is formed, a stator core 8′ is assembled inside the coil package 5′, then a concave arc surface of a concave arc portion of the stator core 8′ is sleeved on an outer arc surface of a wall of a rotor housing 17′ of a pump body 10′, and the coil package 5′ and the pump body 10′ is fixed into one by a snap 18′.
The above alternating-current permanent magnet drainage pump has the following disadvantages. Firstly, since the stator core 8′ is sleeved on the outer wall of the rotor housing 17′ such that the stator core 8′ and the magnetic core 15′ are separated by the rotor housing 17′ (usually, the rotor housing 17′ has a thickness of at least 1 mm due to a requirement for strength), a distance between the concave arc surface of the stator core 8′ and the magnetic core 15′ of the rotor is increased (to at least 1.5 mm), resulting in a larger magnetic air gap and thus a greater magnetic resistance and a lower electromagnetic efficiency. Secondly, there are gaps between the stator core 8′ and the rotor housing 17′, between the stator core and the coil package 5′ and between the coil package 5′ and the pump 10′. Thereby, during operation, noise will be caused by vibration between various parts or components. Thirdly, heat dissipated by the stator core 8′ is thermally conducted only by radiation and to the rotor housing of the pump body 10′, resulting in a poor heat dissipation.